Understanding the role and control of the capacity vessels (veins) in the maintenance of cardiovascular homeostasis is the long-range goal of this project. The immediate objectives are: (1) To evaluate the reflex effect of peripheral chemoreceptor stimulation on the capacitance system by pump-perfusing dogs from a venous return reservoir to maintain a constant cardiac output. The central venous pressure will be held constant. Changes in the reservoir volume will be equal and opposite to the degree of vascular volume change. The carotid bodies will be isolated and perfused at constant pressure with blood of high or low oxygen and/or carbon dioxide tensions. The effects of acidotic blood and systemic hypoxia or asphyxia will also be studied. (2) To develop further and evaluate indicator dilution techniques for measuring changes in capacity vessel volume, dynamics of mixing, and changes in the volume of distribution of erythrocytes and plasma proteins. (3) To quantify the degree and nature of blood volume redistribution during endotoxin shock in dogs. Changes in the circulatory vascular capacitance and blood volume of the liver and other organs will be studied using the pump-perfused preparation and indicator dilution techniques. (4) Computer simulation will be used to summarize data and to evaluate my understanding of interactions of various parts of the system.